The major aim of the current research program is to define under controlled clinical trial conditions the long-term efficacy of phentermine-fenfluramine combination used in conjunction with diet and behavior modification in the treatment of simple moderate obesity. The double-blind phase of the trial comparing combination medication vs. placebo has already been completed and it has clearly demonstrated the significant advantages of the combination medication for weight control. The study is currently in the maintenance phase. The major general outcome variables being followed are weight loss and maintenance of the weight lost. The cardiovascular variables being followed include blood pressure, pulse, standard 12 lead ECG, exercise ECG and lipid profile including total cholesterol, total triglycerides, low-density and high density lipoproteins. In this continuation phase, the research program will explore aspects in relation to the efficacy of continuous vs. intermittent medication, dose-response relationships and the possibility of "resetting" of weight control centers after long-term weight control. The study will provide much new information about many important issues in relation to long-term weight control.